TH400 - Slipping??

[Jeff Kitchen]

I'm curious about something I've noticed my trans doing. It's the car in my sig. Trans is a TH400 built by a local reputable race trans shop. I don't know all of the parts he used on the inside, but I do know it has a JW reverse pattern, manual valvebody. Converter is a PTC 9". I leave off of the footbrake from an idle. Looking at my Playback tach, it flashes to about 4800-5000, goes up to the 1-2 shift at about 6400 (I run a 6200 chip in the air shifter), but it only drops down to about 6000 after the shift. It sits there for a short time and then goes to 6200 and shifts to 3rd. I run through the traps at 6500. So, going down the track, it feels fine in 1st, but it's only in 2nd for about one second. I'm not sure it's slipping because the car leaves hard (1.36 best 60'), is consistent, and MPH's good with consistency. Any thoughts?

One other clue - it seems like all of this started about the same time I switched from regular Castrol ATF to Mobil 1 synthetic ATF. Could that be the cause?

[Hutch]

It certainly sounds like you are having a problem with 2nd gear. Whats the shift drop on the 2-3? If its lower than the 1-2 then that tells me that 2nd gear is slipping.

Let me know, Hutch

[Jeff Kitchen]

Looking back at my playback, it looks like it drops to around 5600 RPM on the 2-3 shift. So, what could it be? Could it be related to the synthetic ATF? It still baffles me that the car has actually gotten faster the last few times out.

Thanks for any help you have.

[Hutch]

I don't think the synthetic oil is the problem. There is likely a problem with the 2nd clutch/pressure plate or case lugs. Do an oil pan inspection first to see if there is any signs of clutch wear, if so you know what to do. this may fit into the old saying, they always run best right before they break.
Let me know what you find

Hutch